1. Field of the Invention
The present invention generally relates to an image forming technique. More particularly, the present invention pertains to a liquid droplet ejecting unit in which plural liquid droplet ejecting sub-units that eject droplets of a liquid fed through a common liquid feed path from nozzles onto a recording medium are arrayed in a direction perpendicular to the conveying direction of the recording medium; an image forming apparatus including this liquid droplet ejecting unit; and a valve that is provided in a vertically extending liquid flow path along which the liquid is fed downward.
2. Description of the Related Art
A structure has conventionally been devised in which a long inkjet recording unit (liquid droplet effecting unit) having a recording region of the width of a recording medium or longer (the length in a direction perpendicular to the conveying direction of the recording medium) and plural short sub-units (liquid droplet ejecting sub-units) having a recording region shorter than the width of the recording medium are arrayed in the widthwise direction of the recording medium.
In the above structure, when the sub-units are connected together via a common ink feed path and a suctioning operation for suctioning the ink from the nozzles is performed on a per sub-unit basis, there is a tendency that a suctioning pressure acts on the remaining sub-units in which no suctioning operation is performed, via the ink feed path. For this reason, a negative pressure occurs due to the ink being caused to flow backward in the remaining sub-units in which no suctioning operation is performed, and thus air is suctioned from the nozzles so that air bubbles are formed, whereby a satisfactory resumption action is prevented.
It has conventionally been proposed to provide a check valve at the ink feed port of an inkjet recording head unit (for example refer to JP-A No. 2002-307716, JP-A No. 4-341854, and JP-A No. 2004-58675). Therefore, in the above-mentioned structure, it might be imagined that formation of air bubbles could be prevented by providing a check valve at the ink feed port of each sub-unit so as to prevent the ink from being caused to flow backward in the other sub-units.
However, in the above-mentioned JP-A No. 2002-307716, JP-A No. 4-341854, and JP-A No. 2004-58675, the specific gravity of a spherical member that opens and closes the check valve is selected to be about equal to that of the ink. For this reason, the spherical member remains submerged in the ink except during a suctioning operation, and after the suctioning operation is started, the spherical member is displaced in following the flow of the ink so as to close the check valve. Obviously, this check valve has poor readiness of the checking operation. Thus, a time lag occurs between when the suctioning operation is started and when the check valve is closed, and there is a problem such that air bubbles occur as a result of ink flowing backward during the time lag.
Meanwhile, it is possible to improve the readiness of the check valve for the checking operation by previously causing the spherical member to be biased in the direction of backward flow of the ink, by means of a spring or the like, as in the case of an ordinary check valve. However, in such a case, there is another problem that an increased pressure loss is caused due to an increase in the load of an opening operation when the ink is fed in a normal direction.